Trigger index means for mercury button switch



y 1963 F. G. VONHOORN ETAL 3,089,937

TRIGGER INDEX MEANS FOR MERCURY BUTTON SWITCH Original Filed Feb. 2, 1959 Z w l/ M 4 acid 2% States This invention, which is a continuation of application Serial No. 790,518, filed February 2, 1959, now abandoned, relates to a mercury button switch and particularly the means for restraining the accidental movement of the switch trigger and imparting a smooth action to the trigger. Mercury button switches have been made for many years according to the teachings in the Sambleson Patent No. 2,142,154, which is assigned to the same assignee as is the present invention.

Heretofore it has been customary to employ an intermediate spring section between the mounting strap and the trigger to serve as a resilient index means and restrain the accidental movement of the trigger. Such spring sections are either integral with the mounting strap or are separate members installed in slots provided for that purpose. 'In both types, however, the tendency toward misalignment, binding, and erratic tripper operation is compounded by the use of the spring action of the mounting strap together with its irregularities in conjunction with the turning action of the button in the switch contacts, and the switch trigger riding on the button.

The principal object of the present invention is to provide a mercury button switch with a simple, flat, noncritical abutment to definethe trigger stop positions and angle :of throw as well as to cushion the trigger action to assure a smooth and silent operation.

A further object of the present invention is to provide a mercury button switch with resilient switch contacts that are relied upon to cushion the movement of the trigger from one extreme position to the other.

A still further object of the present invention is to provide a mercury button switch where the trigger has cam means for engaging the underside of the mounting strap to act as the fixed stops of the trigger and accurately govern its angle of throw.

A further object of the present invention is to provide a mercury button switch with novel screw terminals which are rigidly fastened in the housing and are independent of the spring action of the switch contacts so that the switch may be either side or back wired.

A preferred embodiment of the present invention is illustrated on the accompanying drawing. The switch comprises a recessed base that is closed by a metal mounting strap. Two of the opposing walls of the base have vertical grooves for supporting the ends of a parallel pair of bowed spring contacts. The central portion of each contact has a spherical segment facing inwardly toward the other. Each segment mates within a concavity in the side of a mercury button to act as the pivotal bearing for the button. A switch trigger is seated on the top of the button and is in driving engagement therewith so that movement of the trigger will cause the button to rotate about its central pivotal axis. The mounting strap includes an opening through which the trigger extends. An inverted V-shaped cam is located on each side of the trigger to be in tight rubbing engagement with the underside of the strap. The inclined sides of the cams serve to hold the trigger in one of the two extreme positions. As the trigger is moved out of an extreme position, the cams will press the button downwardly within the base, thereby spreading the spring contacts further apart until the trigger 3,089,937 Patented May 14, 1963 passes over center at which time the spring contacts will tend to move the trigger to the other extreme position.

The screw terminals of this switch are also of novel design. An opening is formed in the two opposing walls of the base which do not include the vertical grooves for the switch contacts mentioned previously. These openings are made adjacent the bottom wall of the base so that the switch may either be side or back wired. Each terminal screw is threaded into an opening in a tab that extends inwardly from one side of the switch contact. The tab is directly below the contact proper and Within the same plane. The innermost end of the tab is fitted within a short vertical groove within the base so that the tab is rigidly held to close the opening in the outer wall of the base. The tab is so designed that the terminal screw may be threaded into the tab and the entire contact assembled in the base at the same time the other contact and the mercury button are assembled.

Our invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

FIG. 1 is a front elevational view of a mercury button switch embodying the present invention.

FIG. 2 is a cross-sectional view taken on the line 2-2 of FIG. 3 to show the interior layout of the switch mechanism.

FIG. 3 is a plan view of the recessed base with the trigger and mounting strap removed to show the nature of the bowed spring contacts when the mercury button is in place.

FIG. 4 is a plan view similar to FIG. 3 with all of the loose parts removed to show the nature of the switch base.

FIG. 5 is a partial view of one of the switch contacts showing its spherical bearing, there being a mercury button also shown with its concave side wall for mating engagement with the bearing.

FIG. 6 is a diagrammatic showing of the depression of the mercury button when the trigger is centrally disposed between its two extreme positions.

Referring in detail to the drawing and in particular to FIG. 1, the switch comprises a recessed base 11 of molded insulating material, a steel mounting strap 12 that closes the opening in the base, and a manually operable switch trigger 13. The main element of the switch is a mercury button 14, shown in FIG. 5, that represents a liquid circuit closure for making and breaking the circuit through the switch. Mercury buttons have become widely ac cepted in the last 20 years so that it is felt unnecessary to go into detail and explain how they are made and how they operate.

It will be understood by those skilled in this art that a mercury button is adapted to rotate about a central axis that extends through the centers of its two side walls. A mercury button is designed to operate within a maximum angle of rotation of 40. Whenever the switch trigger is allowed to traverse a larger angle, the trigger would normally strike the end of the rectangular opening in the faceplate that covers the switch. In so doing, a noise would be emitted which is highly objectionable since mercury switches are sold and used as silent switches as distinguished from the standard snap action toggle switch that gives out a sound resembling the closing action of a mouse trap.

The mercury button 14 is pivotally supported between a pair of bowed spring contacts 15 which are best shown in the top plan view of FIG. 3. The recessed base 11 has a bottom wall 16, opposed side walls 17, and end walls 18. A pair of vertical grooves 19 are formed on the interior of the end walls 18 for supporting the ends of the spring contacts 15. These grooves 19 hold the spring contacts away from the side walls 17 so that the contacts may flex during the movement of the switch trigger 13. The central portion of each contact 15 has a spherical segment 26 extending inwardly toward the complementary segment of the opposite contact. This spherical segment is adapted to mate within a smaller concavity 21 in the side wall of the button 14, as is best illustrated in FIG. 5. Accordingly, the spring action of the contacts 15 will always tend to hold the pivotal axis of the button in alignment with a line drawn between the center of the spherical segments.

The exterior of a mercury button consists of a pair of hat-shaped metal shells 22 with a circular rim 23. The rims 23 on each shell face each other but are separated by and sealed to a glass ring 24 that forms a hermetic seal. The lower end of the switch trigger 13 is enlarged and hollowed out so that it may seat on the curved portion of the shells rather than on the glass ring. Each shell has a depression 25 for receiving a tongue 26 from the underside of the trigger, as will be understood with reference to FIG. 6. This interengagement serves to connect the trigger with the mercury button so that movement of the trigger will effect a rotation of the button on the spherical bearings of the switch contacts.

Means must be provided to hold the trigger in driving relation with the button. This force is represented by the steel mounting strap 12 that is fastened over the open top portion of the base 11 by bendable tabs (not shown) that engage under suitable abutments on the outside of the end walls 18. This mounting strap is of relatively heavy gauge sheet steel and its rigidity is an important factor in the improved operability of this switch. Each side of the trigger 13 that overlies the metal shell 22 is provided with an inverted V-shaped cam surface 27 on its top side. Each cam surface 27 has a central apex 28 and flat diverging surfaces 29. The fiat surfaces 2% serve as fixed stop means to limit the movement of the trigger as the trigger rotates about the pivotal axis of the mercury button 14. In all mercury switches that are assembled in or on the wall of a room the upper position of the trigger is the OFF position. The fiat surfaces also serve as an index means to prevent vibrations in the vicinity of the switch from moving the trigger downwardly in the event that the trigger is in the OFF position.

The trigger is indexed because in order to move it from the position shown in FIG. 2, it is necessary to force the mercury button 14 downwardly against the opposing forces of the bowed spring contacts 15. This downward movement of the button 14 is necessary so that the apex 28 of the cam may swing under the strap 12, as shown in FIG. 6, and then move to the opposite extreme position.

In the manufacture of mercury buttons, the outer casing of the button is formed first and a small hole is left in one of the shells 22 for admitting the mercury and the hydrogen gas. In the final assembly operation, the hole is sealed by a small metal plug 36 that is welded therein, as is seen in FIG. 5. Because this plug 30 extends within the concavity 21 of the shell, it is necessary to provide an aperture 31 in each of the spherical segments 20 of the switch contacts so that there will always be a ball and socket relationship between the segments 20 and the concavities 21. Looking at FIG. 2, the aperture 31 is visible within the spherical segment 20 and the plug 30 is centered within the aperture since the trigger 13 is in one of its two extreme positions. This situation should be compared with that illustrated in FIG. 6 where the trigger 13 is temporarily in its central position with the apex 28 of the earns 27 in line contact with the underside of the strap 12. The plug 30 is shown in a lowered position since the mercury button 14 has been depressed by the cam surfaces of the trigger, thereby spreading the spring contacts 15 apart.

Provision must be made to limit the amount of depression of the mercury button 14. Such a limit means is represented by a pair of cradles 32, best shown in FIGS. 2 and 4, which are projections that extend upwardly from the bottom wall 16 of the base and have curved top portions 33 that are adapted to engage the underside of the shells 22 of the button as the trigger passes through its central position. Such a precaution is necessary because it could happen that a board might fall against the switch and cause the button to spring out from between the contacts, thereby rendering the switch inoperative. There is a slight lifting of the metal strap 12 as the trigger passes through its central position, but most of the resilience in this type of trigger index means is provided by the springing action of the bowed contacts 15.

As previously mentioned, the ends of the spring contacts 15 are located within vertical grooves 19 on the interior of the end walls 18 of the base. The mounting strap 12 is used to hold these contacts down in the base. Thus, small insulation spacers 34 are positioned across the ends of the two contacts 15 and are supported within opposed grooves 35 in the side walls 17 of the base, as is best understood from FIGS. 2, 3, and 4.

Novel screw terminal means are also provided by this invention so that the switch may either be side or back wired. In all mercury button switches manufactured in the last two decades, the terminal screws were located on the top or front face of the switch near the mounting strap, as is exemplified by the Sambleson patent cited above. This invention is the first known development to change the screw terminal means of mercury button switches. In the opposite lower corners of the side walls 17 of the base 11, an opening 36 is formed for gaining access to a terminal screw 37. A slight amount of the bottom wall 16 is cut away, as at 38, while the end wall 18 is cut away at 39 so that a lead wire (not shown) may extend from either the end, bottom or side of the base and be wound around the shank of the screw. Looking at FIG. 2, the terminal screw 37 is threaded into a terminal tab 40 that extends from one end of the spring contact 15 and is directly beneath the contact proper. A short vertical groove 41 is formed near the bottom of the base to support a mating edge of the terminal tab 40 at one side of the opening 36 in the side wall 17. The top portion 42 of the tab 40 is formed over the head of the screw 37 to seal the opening in the base and prevent the lead wire from interfering with the switch mechanism. A study of FIG. 3 will render apparent that it is possible to thread the terminal screw 37 into the 40 before the contact 15 is assembled-in the base. The terminal tab 40 is rigidly supported in the base although the spring contact 15 is allowed to flex as the trigger is thrown from one extreme position to the other.

Having described above our new and improved mercury button switch with a foolproof trigger indexing means, it will be readily apparent to those skilled in this art that the fiat, rigid mounting strap serves as an accurate datum plane from which the indexing of the trigger is accomplished by the cam surfaces on the sides of the trigger. Since the mounting strap is peifectly flat and is not a formed part, with a special arcuate curve as in previous designs, the misalignment of the strap as it is fastened to the base does not injure the alignment of the mercury button and trigger within the housing. We have also devised a unique method of arranging the screw terminal means of the switch within rigid supports in the base. This is important because once the lead wires are fastened to the terminal screws, it is necessary to force the switch back into a switch box. In situations where the lead wires are of large size, and only slightly flexible, there is a tendency for the lead wires to bend the terminal means out of shape. Except for the rigid support of the tabs, the spring tension of the contacts might be affected since they are integral with each other.

Modifications of this invention will occur to those skilled in this art and it is to be understood, therefore, that this invention is not limited to the particular embodiments disclosed but that it is intended to cover all modifications within the true spirit and scope of this invention as claimed.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. A mercury button switch comprising a housing of insulating material with a bottom wall and opposed side and end walls, the housing having an open top portion, two of the opposing walls defining vertical grooves for supporting the ends of a parallel pair of bowed spring contacts, a spring contact positioned in said housing by each pair of vertical grooves, the central portion of each contact having a spherical segment extending toward the other, a mercury button between said spherical segments, each segment mating with a concavity in the side of said mercury button and acting as a pivotal bearing for said button, each spherical segment defining an aperture coaxial with said button, said apertures being of a size to allow movement of said mercury button with reference to said spherical segments, a switch trigger seated on the top of the button and in driving engagement therewith so that movement of the trigger will cause the button to rotate within the contact bearings, a metal mounting strap fastened over the open top portion of the housing, the strap including an opening through which a portion of the trigger extends for manual operation, the trigger having an inverted V-s-haped cam on each side of the button in tight engagement with the underside of the strap, whereby shifting the trigger from one extreme position to the other will cause the cams of the trigger to drive the button down into the housing while spreading the spring contacts further apart, the inclined sides of the cams serving as positive stops to limit the stroke of the trigger.

2. A mercury button switch comprising a hollow housing formed by a recessed base of insulating material and a metal mounting strap, two of the opposing walls of the base having vertical grooves for supporting the ends of a parallel pair of bowed spring contacts, spring contacts in said grooves the central portion of each contact having a spherical segment facing inwardly toward the other, a

mercury button suspended between the segments of the spring contacts, the segments extending into mating concavities within the sides of the mercury button, each segment defining an oversize aperture coaxial with said button, said apertures conferring limited movement on said button with respect to said contacts, a switch trigger seated on the top of the button and in driving engagement therewith so that movement of the trigger will cause the button to rotate on the spherical segments, a mounting strap fastened over the recess in the base, the trigger extending through an opening in the strap for manual operation, the trigger having an inverted V-shaped cam on each side of the button in tight rubbing contact with the underside of the strap, whereby moving the trigger from one extreme position to the other will cause the cams of the trigger to force the mercury button downwardly into the base thereby spreading apart the spring contacts, the inclined sides of the cams acting as positive stops to limit the stroke of the trigger as well as to relieve some of the downward pressure exerted on the button by the trigger.

3. A mercury button switch as recited in claim 2 wherein each spring contact is provided with a screw terminal that is threaded into a terminal portion of the contact, said terminal portion being located beneath one end of the contact proper and extending inwardly from the fixed end of the contact, the terminal portion being positioned between a pair of opposed grooves so that the terminal portion may not be sprung out of shape to cause a reduction in the spring force bearing against the sides of the mercury button, and openings through the walls of the base for gaining access to the screw terminals so that lead wires may be clamped thereunder.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A MERCURY BUTTON SWITCH COMPRISING A HOUSING OF INSULATING MATERIAL WITH A BOTTOM WALL AND OPPOSED SIDE AND END WALLS, THE HOUSING HAVING AN OPEN TOP PORTION, TWO OF THE OPPOSING WALLS DEFINING VERTICAL GROOVES FOR SUPPORTING THE ENDS OF A PARALLEL PAIR OF BOWED SPRING CONTACTS, A SPRING CONTACT POSITIONED IN SAID HOUSING BY EACH PAIR OF VERTICAL GROOVES, THE CENTRAL PORTION OF EACH CONTACT HAVING A SPHERICAL SEGMENT EXTENDING TOWARD THE OTHER, A MERCURY BUTTON BETWEEN SAID SPHERICAL SEGMENTS, EACH SEGMENT MATING WITH A CONCAVITY IN THE SIDE OF SAID MERCURY BUTTON AND ACTING AS A PIVOTAL BEARING FOR SAID BUTTON, EACH SPHERICAL SEGMENT DEFINING AN APERTURE COAXIAL WITH SAID BUTTON, SAID APERTURES BEING OF A SIZE TO ALLOW MOVEMENT OF SAID MERCURY BUTTON WITH REFERENCE TO SAID SPHERICAL SEGMENTS, A SWITCH TRIGGER SEATED ON THE TOP OF THE BUTTON AND IN DRIVING ENGAGEMENT THEREWITH SO THAT MOVEMENT OF THE TRIGGER WILL CAUSE THE BUTTON TO ROTATE WITHIN THE CONTACT BEARINGS, A METAL MOUNTING STRAP FASTENED OVER THE OPEN TOP PORTION OF THE HOUSING, THE STRAP INCLUDING AN OPENING THROUGH WHICH A PORTION OF THE TRIGGER EXTENDS FOR MANUAL OPERATION, THE TRIGGER HAVING AN INVERTED V-SHAPED CAM ON EACH SIDE OF THE BUTTON IN TIGHT ENGAGEMENT WITH THE UNDERSIDE OF THE STRAP, WHEREBY SHIFTING THE TRIGGER FROM ONE EXTREME POSITION TO THE OTHER WILL CAUSE THE CAMS OF THE TRIGGER TO DRIVE THE BUTTON DOWN INTO THE HOUSING WHILE SPREADING THE SPRING CONTACTS FURTHER APART, THE INCLINED SIDES OF THE CAMS SERVING AS POSITIVE STOPS TO LIMIT THE STROKE OF THE TRIGGER. 